This disclosure relates to toners, developers containing the toners, and a method of forming images with the developers utilizing a magnetic brush development system. More in particular, the disclosure relates to toners and developers having controlled properties via a specific external additive set to provide superior print quality and improved admixing of the toner into the developer.
U.S. Pat. No. 6,319,647 describes a toner of toner particles containing at least one binder, at least one colorant, and preferably one or more external additives that is advantageously formed into a developer and used in a magnetic brush development system to achieve consistent, high quality copy images. The toner particles, following triboelectric contact with carrier particles, exhibit a charge per particle diameter (Q/D) of from 0.6 to 0.9 fC/μm and a triboelectric charge of from 20 to 25 μC/g. The toner particles preferably have an average particle diameter of from 7.8 to 8.3 microns. The toner is combined with carrier particles to achieve a developer, the carrier particles preferably having an average diameter of from 45 to 55 microns and including a core of ferrite substantially free of copper and zinc coated with a coating comprising a polyvinylidenefluoride polymer or copolymer and a polymethyl methacrylate polymer or copolymer.
U.S. Pat. No. 6,416,916 describes a toner of toner particles containing at least one binder, at least one colorant, and an external additive package comprised of zinc stearate and at least one of silicon dioxide or titanium dioxide, wherein the amount of zinc stearate is limited to about 0.10 percent by weight or less of the toner. It is reported that when the amount of zinc stearate is so limited, a developer formed from the toner exhibits excellent triboelectric charging and stability and excellent developer flow. When the developer is used in a magnetic brush development system, consistent, high quality copy images are formed substantially without any depletion defects over time.
What is still desired is a toner, preferably for use in magnetic brush development systems, which is able to produce high print quality in all environments. It is also still desired that addition of the toner as an admixture into the developer will not generate any toner that has wrong sign polarity.